FIG. 1 of the accompanying drawings illustrates a standard plug-in expansion card 10 for a computer. The card 10 carries electronic circuitry (not shown) intended to connect with the main computer circuitry through a plug-in edge connector portion 11. Plugging in the card 10 by its connector portion 11 into a connector of the computer serves to locate the card in the computer. However, to retain the card in position and hold it fast, the card is further provided at one end with a metal mounting plate 12. This plate has locating tab 13 at one end and a screw-receiving recess 14 at the other end. The plate may be apertured to enable external access to external connectors mounted on the expansion card.
FIG. 2 shows a typical computer housing structure 15 in the region of mounting of expansion cards inside the computer. In particular, a metal mounting bridge 16 is provided which is adapted to support up to four expansion cards. The mounting bridge 16 is provided with four threaded apertures 17 for receiving fixing screws, one for each expansion card to be secured in position. In addition, the bridge 16 is formed with four rectangular apertures 18, each permitting access to any external connectors provided on an expansion card.
FIG. 3 shows the mounting of two expansion cards 10 on the mounting bridge 16 of the FIG. 2 structure 15. The expansion cards are first plugged by their connector portions into internal electrical connectors mounted on a circuit board extending out at right angles from the housing wall (neither this circuit board nor the connectors are shown as the present invention is not concerned with these elements). At the same time, the locating tab 13 of each card is inserted in a corresponding slot formed in the housing structure (again, this slot is not shown as it is not relevant to the invention). The mounting plate 12 of each card lies against the mounting bridge with the recess 14 of each mounting plate aligned with a corresponding one of the threaded apertures 18 in the mounting bridge 16. A fixing screw 19 is then used to secure each card in position, the screw being engaged in the corresponding aperture 18 and screwed down to clamp the mounting plate of the card against the bridge 16. This clamping also serves to provide a good grounding (earthing) connection between the plate 12 and the mounting bridge 16.
Blanking plates 20 of a form similar to the mounting plates 12 are fixed in position by further screws 19 over the apertures 17 of the bridge 16 for which there are no corresponding expansion cards.
This prior art arrangement for securing expansion cards in position is somewhat cumbersome for unskilled users who may drop the fixing screws inside the computer or may find it difficult to screw in the screws 19 (the close presence of the housing hindering turning of the screws by hand). The need to have multiple fixing screws where multiple expansion card slots are present is also inconvenient.
FIG. 4 shows one known arrangement for overcoming some of the problems presented by the traditional way of securing expansion cards in position. In the FIG. 4 arrangement, a clamping bar 40 provided with clamping fingers 41 is used to secure in position a plurality of expansion cards/blanking plates (for reasons of clarity, only one card 10 is illustrated). More particularly, the fingers 41 serve to clamp the card mounting plates 12/blanking plates against a bridge structure 16 of the housing 15. At each end of the clamping bar 40 is a side pillar 42 that supports the bar on the top of the bridge structure 16. Each pillar 42 has a depending spigot 43 that is located in an aperture 44 in the bridge structure 16. The spigots 43 serve to position the bar and to define an axis A about which the bar can be pivoted in a direction indicated by arrow B to move the bar 40 from an inclined position (in which it resides when the spigots are first introduced into the apertures 44) to an upright position shown in FIG. 4. In the latter position, a snap-engagement member 45 provided on top of the bar 40, snap engages in an aperture 46 formed in the housing 15. In use, once the card 10 has been placed in position, the spigots of the clamping bar 40 are inserted into the apertures 44 and the bar is then pivoted into its upright position to move a corresponding one of the fingers into clamping engagement with the mounting plate 12 of card. When upright, the bar 40 snap engages into position. The bar 40 is made of a plastics material and in order to facilitate electrical grounding of the mounting plate 12, a thin metal grounding finger can be provided beneath each finger 41, these grounding fingers being electrically connected to a contact that is pressed against the housing when the bar is in its snap-engaged position.
Although the FIG. 4 arrangement facilitates the secural of multiple cards and avoids the risk of fixing screws being lost inside the housing, a number of drawbacks still exist. Thus, the need to provide side pillars to support pivoting movement of the bar means that the extent of the mounting bridge is greater than otherwise needed--this makes the arrangement unsuitable for use where space is at a premium (for example, it would be difficult to use the arrangement in the FIG. 2 situation). Furthermore, the magnitude of clamping pressures obtainable using the FIG. 4 arrangement is generally not as great as can be achieved with a screw mechanism which also has the benefit of adjustability. Finally, the need to provide a complex plastics part (the bar 40) and a separate metal grounding part, increases the cost of the securing arrangement.
It is an object of the present invention to provide an arrangement for securing an expansion card (or other user-installable unit) that overcomes at least some of the disadvantages of the prior art.